1. Field of the Invention
The present invention relates to an optical phase controller which controls a phase at a predetermined wavelength or wavelength band, and an optical phase control method.
2. Description of the Related Art
Materials with birefringence, such as quartz, calcite, polymer stretch films, and the like, have been used for wave plates.
Such materials have optical axes of ordinary light and extraordinary light and the propagation velocity of incident light varies according to the optical axes because refractive index varies according to the optical axes.
Therefore, a phase difference occurs in light transmitted through such a material. In order to allow the material to function as a wave plate, a ½ wave plate and a ¼ wave plate require a phase difference of 180° and a phase difference of 90°, respectively, and thus require thicknesses corresponding to the phase differences.
Wave plates having such characteristics are used for various optical devices and measurements, such as antireflection of pickup lenses and lasers of CD, DVD, and the like, optical measurements such as ellipsometry, laser interferometers, optical shutters, image projectors such as liquid crystal projectors and the like.
When a wave plate is used for antireflection of pickup lenses and lasers of CD, DVD, and the like, the wave plate may function for only the wavelength of output light. However, a wave plate having a wavelength band may be required for ellipsometry, liquid crystal projectors, and the like.
A material having birefringence has been allowed to function as a wave plate. However, in this case, it is difficult to achieve a wide band in view of the wavelength dispersion of the material.
In order to resolve this problem, a wave plate referred to as an “achromatic wave plate” has been developed, in which a plurality of wave plates are combined so that the optical axes are perpendicular to each other.
This wave plate permits a relatively wide wavelength band to be realized by combining materials having different wavelength dispersions (refer to, for example, Japanese Patent Laid-Open No. 11-337733).
In addition, US 2006/0262398A proposes a polarization control element which controls polarization using the fact that a phase difference occurs between metal microstructures due to near-field interaction between the metal microstructures.
In the achromatic wave plate disclosed in Japanese Patent Laid-Open No. 11-337733, a plurality of materials are combined so that the optical axes are perpendicular to each other, and thus combining accuracy is important.
In addition, the materials for the wave plate are limited to those having birefringence, and thus the cost is increased. Further, since a difference in refractive index between ordinary light and extraordinary light is small, the thickness of the wave plate is increased for achieving a predetermined phase difference, thereby causing limitation of the degree of freedom of design.
Further, when a wave plate using an organic material such as a polymer stretch film or the like is used for an optical device with large light source energy, such as a projector, a problem with heat resistance and light resistance may occur.
Further, in the polarization control element using at least two metal microstructures disclosed in US 2006/0262398A, the strength of near-field interaction can be controlled by adjusting the distance between the metal microstructures, thereby permitting polarization control with a high degree of design freedom.
However, when used for a wave plate, a sufficient phase difference (e.g., a phase difference of 90° for a ¼ wave plate) is required, it is thought to be necessary that a distance between the metal microstructures is several nm.
In order to form the element while controlling the distance between the metal microstructures to several nm, high precision is required, and thus variation easily occurs in the distance between the metal microstructures, thereby failing to perform predetermined polarization control. It is also pointed out that the production cost is increased.